Examples: post #477959, post #566480, post #690746, post #757350, post #805607

There is the existing hairstyle_switch tag, but it doesn't feel applicable on post #566480 and post #805607 where Mio isn't showing her forehead like Ritsu's hairstyle. costume_switch would seem a bit too much for a single ornament too.

I just created hairband_removed, but given there are other kinds of hair ornaments to be removed and I can't find any tags for them so far, perhaps a more general hair_ornament_removed tag should be used instead? That in turn can be implicated to headwear_removed.

Too specific. Hairband doesn't currently count as a hair_ornament ( link ). Using headwear_removed for anything you would wear on your head is fine enough.

To cover *switch, hat_switch can either be aliased to or implicate a new headwear_switch tag. Given that often only one of the characters wears a hat and the other wears a hairband, hair_bow or similar, I'd go with alias.
Examples: post #587706, post #450137

S1eth said:
Too specific. Hairband doesn't currently count as a hair_ornament ( link ).

Oh wow, should have been paying closer attention. I think it probably should count as "hair ornament", given all else that does, but I don't really have a strong opinion either way.

To cover *switch, hat_switch can either be aliased to or implicate a new headwear_switch tag. Given that often only one of the characters wears a hat and the other wears a hairband, hair_bow or similar, I'd go with alias.
Examples: post #587706, post #450137

Good point, and I would support that alias.

Yeah, headwear_switch sounds good.

Aliased hat_switch to headwear_switch